Core structure



H. V. PUTMAN CORE STRUCTURE May 4, 1943.

Filed Aug. 17, 1940 INVENTOR WlTN ESSES:

Patented May 4, 1943 CORE STRUCTURE Henry V. Putman, S-liaron, Pa.,assigner to Westinghouse Electric &`Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application August I7,1940, Serial No. 353,024

The invention relates, generally, to core structures and, moreparticularly, to core structures having butt joints suitable for use indielectrics.

In the operation of transformers and other lnductive apparatus utilizingmagnetic cores immersed in dielectrics, considerable difiiculty has beenexperienced with joints having worked faces. This results from the oilor other dielectric becoming acid in the course of time with the resultthat the acid dielectric attacks the iron.

The object of the invention is to provide in cores to be used indielectrics a butt joint having a worked face which is protected fromthe dielectric and acids that may be developed.

It is also an object of the invention to provide a core structure inwhich the eddy current losses are small.

Other objects of the invention will, in obvious and, in part, appearhereinafter.

'Ihe invention, accordingly, is disclosed in the accompanying drawingand comprises the feapart, be

tures of construction, combination of elements,

and arrangement of parts which will be exemplified in the structurehereinafter set forth and the scope of the application of which Awill beindicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference may be had to the following detailed description taken inconnection with the accompanying drawing, in which:

Figure l is a view in perspective of a plurality of bonded core sectionshaving worked faces assembled in accordance with the present invention;and

Fig. 2 is'a view in perspective showing how the worked vfaces may bedrawn together to give a predetermined thickness of the oil and acidresisting material.

A butt joint in a magnetic core may cause such high eddy current lossesthat the application of the core is limited and it has no place inelectrical apparatus which is required to be eflicient. The eddycurrentswhich result from contacts in the butt joint can be reduced tothe point where the eddy current losses are small and the core may beutilized without noticeably lowering the efliclency of the electricalapparatus.

ln the making of butt joints it has been found to be desirable to workthe meeting faces of the core sections in order to get a smooth surface.In working the faces the usual practice is to grind the surfaces to thedesired contour. In the grinding operation burrs ,are produced which insome instances may extend between the lamina- 7 Claims. (Cl. F75- 356)-tions of the core sections. These burrs are objectionable since theyestablish electrical connection between adjacent laminations.

'Ihe burrs may be removed by etching or any method known to the art. Inorder to etch the burrs away it may be necessary to impregnate thelaminations constituting a core with some acidresisting material toprevent the acid from penetrating between the laminations. An etchingmethod set forth in the copending application Serial No. 295,750 filedSeptember 20, 1939, now Patent No. 2,293,951, August 25, 1942', in thename of Seastone et al. and assigned to the Westinghouse Electric &Manufacturing Company may be employed.

When the core section has been prepared in this manner, the surfaceoxide or silicate films which ordinarily protect the laminated magneticmaterial from acids and the like are completely removed from the corefaces. Therefore, when such material is immersed in a dielectric whichupon continued use may become acid, there is a possibility that the aciddielectric will attack the worked faces.

In the present invention, an acid and cilresisting thermoplastic resini0 is applied to the worked faces of the core shown generally at H. Manydifferent oil and acid-resisting thermoplastic resins are available.Good results have been obtained by using certain resins sold to thetrade as Bakelite. Experience indicates that the worked faces may beproperly protected by the use of one or more of phenol aldehyde, alkyd,vinyl, or other suitable resins of this type.

It is found to be good practice to paint the worked faces with thethermoplastic resin selected. In the preparation of the thermoplasticresin, it will be prepared of the proper consistency io facilitatepainting and of a softness which will permit the reducing of it to-apredetermined thickness.

Any suitable method may be employed to bring the core faces together toreduce the thermoplastic material to the predetermined thicknesssuitable for the structure being built. In the perspective showing ofFig. 2 a signode strap or band I 2 is provided for drawing the workedfaces toward one another to reduce the thickness of the thermoplasticmaterial I0.

signode straps i2 may be applied to the assembled sections of the corestructure Il to take the place of clamping members. tween the faces ofthe butt joint resulting from the use of the signode strap increaseswhen the transformer is placed in an oven for the purpose The pressurebeof drying it. Stresses of the-order of 25,000.

pounds per square inch are developed in the slgnode straps i2. It hasbeen found that when stresses of -this order are developed that theresin in the butt joint is reduced to e. satisfactoryV core sections maythen be assembled on the coil Il, subjecting them to pressure by meansof signode straps. After the assembling operation, the transformer isheat-treated to effect the well known drying operation. The heating willresult in the thermoplastic material bonding the core sections togethergiving a core which is not subject to attack from an acid dielectric.

The Worked faces of the core sections lmay be brought together to reducethethickness of the applied varnish to the predetermined amount suitablefor the particular apparatus by energizing the coil I3 on the core withdirect current. This latter method lends itself to shop practicewherever direct current is available and gives excellent results. Othermethods of appylingl,

There- The cost of the making `which permitsthe tensionin the bands tobring the faces still closer together there was a further reduction inthe apparent watts loss to 251. The reduction in the eddy currents inthe faces due to the insulating eect of the acid resistant material isshown in thereduction of the true watts loss from 68.8 to 64.6.v

' illustrated example constitutes a practical emthe followingspeciiicationhave shown satisfacl.

example.y

assembly. l Signode bands-Applied to iron circuits separately.

Approxi- Apparent Truewatts matetem wattsloss loss Demme Acid resistantmaterial on A' C'.

bodiment ofmy invention, I do not limit myself to the exactdetailsdescribed since the materials may be considerably varied withoutdeparting from the spirit ofthe invention as defined in the appendedclaims'. y

I claiml as my invention:

'1. In a transformer, in combination, a plurality of core sections,worked and etched faces for making a butt joint on the core sections,and an acid-resistant material applied to the faces, the faces beingbrought together in the making of a butt joint to reduce theacid-resistant material to a predetermined thickness.

2. In a transformer, in combination, a plu'- rality of core sectionsbuilt up from laminations of magnetic material, bending material forbendsponsiveto temperature to effect the bonding of `the core sectionsto one another during-the v i drying of the transformer by subjectingitl to a heat-treatment. v

3. Ina transformer, in combination, a `plu.

rality of core sections comprising a plurality of laminations ofmagnetic material bonded to-one another, faces on the core sectionsWorked and etched for the purpose of making a butt Joint and a resinselected from the group consisting of a phenol aldehyde, alkyd, or vinyltype of resin applied to the Worked faces of the core sections.

the resin being ofsuch character that it may be reduced to apredetermined thickness under pressure applied to the core sections anddried, bonding the core sections to one another by the subjecting of thetransformer to a heat-treatment to dry it.

'4. A butt joint for velectrical apparatus com-,

prising a yplurality of core sections built up of laminations` ofmagnetic material bonded together,l faces provided on the core sections,the faces being `Worked and etched to give the proper contour andremovebuns, and anacid and oilresisting resin applied to the worked and etchedIt will be noted in the foregoing report on per-V l formance thatapplying the acid resistant material to the worked faces of the coreresulted in A an increased air gap which caused the apparent watts lossto increase from 264 to 2,90. Applying the bands under tension broughtapparent watts loss down to 282, and after the heating in the ovenfaces, .the resin being of a character to lend itselfto the bonding ofthe worked faces when subjected to heat.y

5.In a'f transformer core' structure, in combination, aplurality of'coresections'built up from` laminations-of magnetic material,acid'resistantv bonding material for bonding the laminations to onevanother in themaking of the core sections, facesworked on the coresections for the making of a'butt joint, and an acid resistant. l

another to compress the thermoplastic material to give van insulatingnlm, the .thermoplastic material being responsive to temperature toeffect the bonding of the worked faces of the core sections to oneanother.

6. In a transformer core structure, in combination, a plurality of coresections comprising groups of laminations of magnetic material, resinousmaterial for bonding the laminations to one another in the making of thecore sections, faces worked on the core sections for the making of abutt joint, an acid resistant thermoplastic material disposed betweenthe worked faces of the core sections and a binding member applied tothe core sections for drawing the worked faces toward one another tocompress the thermoplastic material to provide a nlm, the thermoplasticmaterial being responsive to temperature and capable of bonding theworked faces of the core sections to one another.

7. In a transformer core structure, in comblnation, a plurality of coresections comprising groups of laminations of magnetic material, aresinous material for bonding the laminations to one another in themaking of the core sections, faces worked on the core sections for themaking of a butt joint, an acid resistant thermoplastic materialdisposed between the worked faces and a binding member applied to thecore sections for drawing the worked faces toward one another tocompress the thermoplastic material to provide a lm between the workedfaces of the order of .00025 inch in thickness, the thermoplasticmaterial being responsive to temperature and capable of bonding theworked faces of the core sections to one another.

HENRY V. PUTMAN.

